1. Field of the Invention
The present invention relates to a stator for a flat armature winding type brushless DC motor, the so-called gap winding type electric motor, for use in FA (Factory Automation) and OA (Office Automation), and the gap winding type electric motor using the stator.
2. Description of Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
In a conventional electric motor, a rotation detector is arranged at a position sufficiently distant from the motor electromagnetic portion. For example, such a rotation detector is attached to the non-load side bracket of the motor so as to be away from and opposite to the motor electromagnetic portion.
FIG. 4 shows a schematic cross-sectional view of a conventional motor taken along the vertical plane passing through the motor shaft. In FIG. 4, the reference numeral 41 denotes a stator, 42 denotes a rotor, 43 denotes a frame, 44 denotes a rotation detector printed circuit board, 45 denotes a bracket, 46 denotes a bracket, and 47 denotes a detector cover.
The stator 41 is formed by arranging a plurality of concentrated winding coils in the stator core at regular intervals and sealing the coils and wire connection portions with resin. This stator 41 is inserted in and fixed to the frame 43 with brackets 45 and 46 attached to the ends of the frame 43. The reference numeral 44 denotes a rotation detector printed circuit board arranged at the side of the non-loaded side bracket 45.
The frame 43 is made from a conductive material such as, e.g., iron and grounded via an external wiring. The frame 43 and the brackets 45 and 46 are electrically connected with each other to avoid leaking switching noise generated from the coil connection portion.
As discussed above, in a conventional motor, the rotation detector printed circuit board 44 is arranged outside the stator 41 as a noise prevention measure.
As such a noise prevention measure, it is also known to shield the rotation detector printed circuit board as disclosed by Japanese Unexamined Laid-open Patent Publication No. 2000-333395. However, this document is directed to a special type of a stator which easily generates noise. Specifically, in this stator, a multilayer printed circuit board is arranged at the axial end of the stator core of the motor, and wires are wound on the stator core and the multilayer printed circuit board, in a toroidal manner. In this structure, it is inevitable to shield the rotation detector printed circuit board.
On the other hand, there is another type of motor in which concentrated winding coils are arranged on the inner peripheral surface of the stator core at regular intervals, and the multilayer printed circuit board is not wound by the concentrated winding coils. In other words, the multilayer printed circuit board and the concentrated winding coils are not closely arranged. Thus, the printed circuit board is not required to be shielded as taught by the aforementioned Patent Document.
As the noise prevention measure, it is sufficient to ground the bracket to prevent the rotation detector printed circuit board 44 from being affected by noise generated from a stator coil connection portion.
Specifically, as illustrated in FIG. 4, the rotation detector printed circuit board 44 is arranged at the external side of the non-load side bracket 45. The frame 43 is electrically connected to both the brackets 45 and 46, the frame 43 and the brackets 45 and 46 being made of a conductive material such as, e.g., iron. The frame 43 is grounded via an external wiring. Thus, the leaking of switching noise can be prevented.
As explained above, in a conventional motor of this type, since the rotation detector printed circuit board 44 is arranged outside the stator 41, it was difficult to reduce the size of the motor and decrease the number of constituent parts, resulting in increased cost.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.